Atmospheric concentrations of CO2 and N2O, the #1 and #2 most consequential greenhouse gases on earth, both are regulated in part by metalloproteins containing multimetallic copper-sulfide active sites. The nature of multimetallic cooperativity in these active sites and the role of the conserved copper-sulfide structure as it relates to enzymatic function are poorly understood. The objective of this application is to use synthetic model studies to understand the role of nature's privileged copper-sulfide cluster motif in facilitating multimetallic cooperativity associated with multielectron/multiproton regulation of both CO2 and N2O. Our central hypothesis is that the bridging sulfur atoms both covalently mediate redox coupling of the individual metal sites, and also participate in covalent activation of the small molecule substrates. Our rationale for pursuing this objective is that it will inform and motivate future catalyst designs for crucial multielectron redox transformations that depend on CO2, N2O, and other small-molecule substrates. We will work towards achieving the overall objective by pursuing the following specific aims: 1) develop synthetic methods for tetracopper, dicopper, and copper-molybdenum clusters with single sulfur atom bridges; 2) conduct combined spectroscopic- computational studies of electronic structure across different cluster oxidation states; 3) investigate stoichiometric and catalytic reactions with CO2, N2O, and related model substrates. The proposed research is significant because the synthetic difficulty in accessing such model complexes has precluded their careful study until now, and so our team is in a unique position to make important contributions that advance the field vertically. This approach is innovative because it gives us a unique ability to address biologically relevant coordination chemistry questions with structurally faithful model systems constructed through rational design. Attaining the objective of the proposal will positively impact the chemical community, as multielectron/multiproton transformations of small molecules are crucial not only to biological systems but also to many frontier areas including alternative energy conversion and storage.